Loud speaker



Oct. 2, 1928. 1,685,979

P. H. BRACE LOUD S PEAKER Filed Aug. 6, 1925 WITNESSES: INVENTOR Patented Oct. 2, 1928.

UNITED STATES 1,685,979 PATENT OFFICE.

PORTER H. BRACE, 0F WILKINSBURG, PENNSYLVANIA, ASSIGNOR T0 WESTING- HOUSE,ELEOTRIC 86 MANUFACTURING COMPANY, A CORPORATION OF PENNSYL- VANIA.

LOUD SPEAKER.

Application filed August 6, 1925. Serial No. 48,438.

My invention relates to sound-translating devices and particularly to sound-translating devices having special adaptability for the translation of, electrical energy of substantial ma nitudes.

An 0 ject of my invention is to produce a loud-speaking telephone having a large conical diaphragm member.

Another object of my invention is to pro duce a loud-speaking telephone having a large diaphragm and a relatively large permanent magnet having relatively low coercive force.

Another object of my invention is to provide an electro-dynamic loud-speaking telephone having a diaphragm and a coil, adapted to actuate the diaphragm, and having a diameter greater than the diameter of the diaphragm.

Another object of my invention is to provide a telephone-receiver device having a toroidal permanentmagnet provided with a cylindrical air gap, and a movable coil positioned therein.

In the construction of telephone receivers, it has been found desirable to use a permanent magnet cooperating with an electromagnet.

It has been found desirable to employ as large a value of permanent flux as possible in order to obtain satisfactory sound reproduction, and to obtain adequate efiiciency of translation. I

For purpose of producing sound of large volume, it has also been found desirable to construct telephone receivers on an electro-dynamic principle embodying a movable coil attached to a diaphragm, and positioned in a steady strong magnetic field. It has usually been considered necessary, in utilizing electrodynamic principle, to supply the steady flux by means of an electromagnet in order that it may be sufiiciently large. Attempts have also been made. to utilize cobalt steels of extremely high coercive force for producing the steady flux but high-cost has prevented extensive use of such materials.

The usual prior construction has embodied a magnet having relatively small pole pieces and a relatively small movable coil, it being considered necessary to make the coil as light as possible. The total flux produced by the coilis limited by the available vibratory ourrent, and the amount of winding in the coil. B th are small, and, in order to get the (lee sired pull, a strong steady flux has been necessary. The strong flux and the small pole pieces have thus resulted in high flux densities in the air gap, usually in the neigh borhood of 10,000 gausses. This is difiicult to produce Without the expenditure of considerable energy. However, the same number of maxwells through a much larger area of air gap will produce the same pull upon a suitable coil, and resulting smaller flux density is much easier to obtain.

My invention provides a relatively large toroidal permanent magnet which may conveniently be made of ordinary carbon, carbon-tungsten. or carbon-chromium, magnet steel and which, when so made, has sufficient volume to furnish the necessary magnetic field. The toroidal permanent magnet member of my invention has a cylindrical air gap upon one side thereof in which is positioned a relatively large coil having a relatively small number of turns. This coil is attached to the outer periphery of the sound-radiating diaphragm, and is adapted to conduct the vibratory currents. The coil is caused to move by the reaction between the currents flowing therethrough and the steady flux of the magnet, and to vibrate the diaphragm for the production of sound.

Other objects and structural details of my invention will be apparent from the following description, when read in connection with the accompaying drawing in which,

Figure 1 is a view, in vertical section, of an embodiment of my invention; and

Fig. 2 is a view inelevation of the same embodiment.

In the figures. a toroidal magnet 1 is provided having circular pole pieces 2 and 3 separated by an air gap 4. Within the air gap is positioned a coil 5 which is attached to the periphery of a conical sound radiator 6 which may be of heavy hard paper, micarta or other suitable substance.

The sound-radiating cone 6 is supported from the pole piece 3 by a flexible support member 7 which maintains the coil 5 concentrically within the air gap 4. The supporting means 7 which may be of soft leather is held in position by a frame 8. Lead wires 9 and 10 are attached to the terminals of the coil 5 and to a supply of vibratory electrical energy, such as a radio receiving set or a microphone assembly.

The structure Shown Fig. 1 may conveniently be mounted upon a stand 11, as shown in Fig. 2.

In the operation of my device, the neces sary high magnetic field is provided by the ample bulk of the permanent magnet 1. Facility for using a large length of wire in the coil 5 is provided by its relatively great diameter. This construction therefore requires the use of a relatively small number of turns. The wire of large length cooperating with the high magnetic force, enables the necessary driving force to be obtained from the pulsating electric current of small order used in a radio receiving set. The actuating coil is attached to a conical radiator which is highly desirable for converting the vibratory energy into sound waves.

By my invention, I am enabled to provide a telephone receiver device in which the steady permanent flux is furnished by a relatively inexpensive permanent magnet, in which the current-carrying element is relatively much more effective than in the ordinary construction, and in which a highly ei:'-

ficient sound radiator is embodied.

.Vhile I have shown but a single embodiment of my invention, it is capable of other changes and modifications and it is desired, therefore, that only such limitations shall be imposed thereon as are required by the prior art or indicated by the appended claims.

I claim as my invention:

1. A telephonic receiver device comprising a relatively large circular trough shaped permanent magnet structure having mag netic poles upon opposite edges of the trough, a concentric pole piece attached to said magnet, and a movable coil positioned substantially concentric with said magnet and having a sound radiating diaphragm means attached thereto, the diameter of said radiating means being greater than five inches.

2. A telephonic receiver device comprising a magnet having an air gap, a coil positioned in said air gap and a diaphragm attached to said coil, said magnet having a volume sutficientlylarge to supply a field of the order of 10,000 gausses or more across said air gap, said coil having a diameter substantially as great as said magnet structure and having a small number of turns of wire, said diaphragm having a diameter substantially equal to the diameter of said coil.

3. A telephonic receiver device comprising a sound-radiating diaphragm, a helical coil attached to the periphery thereof and a relatively large toroidal permanent-magnet structure having one pole exteriorly of said coil and another pole interiorly thereof and adapted to produce a cylindrical magnetic field having its lines of force radially disposed, said magnet having a volume sufiiciently large to supply a field of the order of 10,000 gausses between said poles.

4- A telephonic receiver device comprising a toroidal magnet structure having a diameter greater than five inches and being provided with a coaxial circular slot, a diaphragm having a diameter which is substantially equal to the diameter of said slot, a voice-current coil afiixed to and supported by said diaphragm, and resilient means carried by said magnet structure intermediate said slot and the axis of said toroid for centering said voice current coil in said slot, said resilient means serving to supply the sole restoring force to said diaphragm.

5. A telephonic receiver device comprising a toroidal magnet having a diameter greater than five inches and being provided with a coaxial circular slot, a circular pole piece carried by the inner edge of said slot to restrict the opening thereof, a diaphragm having a diameter which is substantially equal to the diameter of said restricted slot, a voice current coil afiixed to and supported by said diaphragm, and resilient means carried by said pole-piece intermediate said slot and the axis of said toroid for centering said voice current coil in said slot, said resilint means serving to supply the sole restoring force to said diaphragm,

In testimony whereof, I have hereunto subscribed my 1925.

PORTER H. BRACE.

name this 24th day of Ju y, 

